Telephone mouthpiece attachment



May 18, 1937- H. L. WHITTAKER ET AL 2,080,552

TELEPHONE MOUTHPIECE ATTACHMENT Original Filed Feb. 26, 1954 inventor:

Patented May 18, 1937 UNITED STATES TELEPHONE MOUTHPIECE ATTACHMENTHarry L. Whittaker, Ville La Salle, Quebec, and William H. Hurford,Montcbelio, Quebec,

Canada Application February 26, 934, S al NO- 7 2, 3 Renewed March 23,1937 5 Claims.

The present invention relates to an attachment for telephones, and moreparticularly to a device attachable to the mouthpiece for the purpose offacilitating conversations.

It is well known that background noises greatly affecttheclarity oftelephonic communications, especially in the case of noisy surroundingssuch as a machine shop, busy office, stores and the like.

It is known also that these noises affect clarity both at the receptionand transmission ends, due to the fact that these disturbances arepicked up by themicrophone and transferred to the receivers at both endsof the telephone line.

In fact, it has been proved that conversations may be carried outsatisfactorily, even among very noisy surroundings, if the microphone atthe noisy end be disconnected or otherwise rendered inactive by means ofa foot switch, for example. Furthermore, the usual booths have beenprovided primarily to isolate these noises, besides insuring privacy.

A study of the problem by the applicants has disclosed the fact that, asmight be expected, the annoying background noises are mostly comprisedof high-frequency sounds much above the frequencies comprised within thescale of the average human voice. Therefore, the problem lay infiltering these undesired vibrations exclusive of the useful voicefrequencies.

Although similar requirements are easily met in electrical circuits bymeans of traps and condensers, such devices in the case of telephoneswere out of the question, primarily because it would be materiallyimpossible to convince the companies to change, or alter, their presentequipment, and also because it was desired to produce an attachmentapplicable to existing material at a cost exceedingly low, and in thesimplest possible manner.

Thus, the problem resolves itself to one of mechanical solution, ifpossible.

The present invention. provides means satisfactorily meeting therequiements of a device for eliminating background noises, which devicecan be attached easily to an ordinary telephone, the cost beingnegligible.

Briefly, the invention consists in the provision of means disposed infront of the telephone mouthpiece, to filter the sounds impinging on themicrophone diaphragm.

Thus, cork has been found eminently successful in its properties ofabsorbing high frequen cies normally above the scale of the human voice.Other materials, of course, can be used with sat isfactcry results, suchas matted and rubberloaded felt, pulp-board, etc.

However, the use of such an absorbing pad alone, in front of themouthpiece, does not quite solve the problem in that the sound-absorbingproperties of these materials are not defined sufficiently well. Inother words, the high frequencies are very well dispensed with, but agood portion of the lower frequencies comprised within the human voicescale are also absorbed. The result is that the human voice is greatlydistorted and talking must be conducted in much louder tones.

To obviate this difficulty, it has been necessary to devise means tocarry directly through the absorbing pad a certain amount of audiblefrequenci-es, by means of a metal, for instance, or other soundconductor of suitable characteristics.

With this purpose in mind, a metal member has been added to theattachment to act as a sound conductor and baffle. This member issecured directly to a base plate acting as a supporting member for theabsorbing pad. The characteristics of this plate must be chosen so thatits natural period of vibration is below the lower portion of the humanvoice scale.

As an example, an attachment according to the invention is shown in theattached drawing, wherein:

Figure 1 is a perspective View of the device attached to a telephonemouthpiece,

Figure 2 is a front view of the attachment in place on the mouthpiece,

Figure 3 is a perspective view of the device alone, before bending atthe attachment lugs,

Figure 4 is a sectional view through the device and mouthpiece, and

Figure 5 is a sectional view through the mouth piece only, showing themethod of attachment.

In the drawing, wherein for the purpose of illustration is shown apreferred embodiment of the invention, the letter A generaily designatesa conventional telephone transmitter having the usual belled mouthpieceit connected therewith.

The attachment constituting the present invention embodies a base plate52, in the present instance in the form of a perforated flat nietallicdisc provided at the periphery with a plurality of radial prongs or cars63 disposed to be bent over the rim of the mouthpiece to secure thedevice in position. This plate or disc [2 is made of a dense metal suchas copper which has been found to give excellent results. As statedpreviously, the metal chosen should be of a thickness and havecharacteristics, such that undesirable periodic vibrations be preventedwithin the scale of the human voice. Since the number and size ofperforations has a direct bearing on the fundamental vibration period ofplate i2, it is evident that thickness alone is not a limiting factor.Thus, thickening of the plate, or increasing the number and size ofapertures, achieves the same result. Therefore, certain experimentationis necessary to obtain the required properties. A plate approximately ofan inch thick, however, and perforated substantially as shown in Figure2 should give good results.

At the inner face of the disc !2 is formed a frustoconical flange l5constituting a directing or baflie member and acting as retainer for theabsorbing means.

Against the inner face of the disc I2 is positioned an absorbing pad I!preferably comprising a disc formed of cork or other material suitableto absorb high-frequency background noises during the operation of thetelephone.

A packing ring l8 which may also be formed of cork or other yieldingmaterial is disposed about the base of the flange l5 and snugly fittedbetween the flange and the outer portion of the telephone mouthpiece ID,in order to effect a tight closure and to prevent metal-to-mouthpiececontact.

Thus, it will be evident that the device of the invention is simple andis based on theoretically correct principles. In practice, the testsconducted have amply proven the capabilities of the attachment to filterall sounds above a given maximum and to facilitate intelligentconversation in noisy surroundings.

As an example, a test may be mentioned of a telephone conversation heldover a country line of several miles length, at which time a groceryorder involving twenty items was given without a single repeat, while aphonograph was playing at good volume at a distance from the telephoneof less than six feet.

It is to be understood that the form of our invention herein shown anddescribed is to be t ken as a preferred example of the same, and thatvarious changes as to the shape, size and arrangement of parts may beresorted to without departing from the spirit of the invention or thescope of the subjoined claims.

Having thus described our claim:-

1. An attachment for the mouthpiece of a teleph ne comprising a baseplate having means for securing the same to the outer end of a telephonemouthpiece and provided with apertures, a highfrequency sound cuttingoif pad secured against the inner face of the base plate, and vibratorymeans extending through said pad from the base plate.

2. An attachment of the character described comprising a base platehaving perforations and means to secure the same to the outer end of atelephone mouthpiece, a cork pad secured against the inner face of thebase plate, and a sound conducting member secured to the plate andextending through the pad.

invention, we

3. An attachment of the character described comprising a base platehaving perforations and securing means for a telephone mouthpiece, saidbase plate being comprised of a soft metal such as copper and thethickness of which and perforations thereof being calculated to lowerthe natural vibration period thereof below the frequency scale of thehuman voice, a sound absorbing pad against said plate, and an extensionmember on the plate extending through said pad, inwardly.

4. An attachment for the mouthpiece of a telephone comprising aperforated rigid disc, ears formed at the edge of the disc fordetachably connecting the same to the outer end of a telephonemouthpiece, a frustoconical flange projecting inwardly from the innerface of the disc, a pad of high-frequency sound absorbing materialsecured against the inner face of the perforated disc, and a packingring snugly fitted between the exterior of the flange and the outer endportion of the mouthpiece.

5. In combination with a telephone mouthpiece, a perforated plate, ahigh-frequency-sound absorbing pad mounted against said plate, and a.metallic member extending through said pad in order to transmittherethrough frequencies comprised within the scale of the human voice.

HARRY L. WHI'ITAKER. WILLIAM H. HURFORD.

